Magnesium base alloy



Patented Jan. 13, 1942 MAGNESIUM BASE ALLOY John C. McDonald, Midland, Mich asslgnor to The Dow Chemical Company, Midland, Mich a corporation of Michigan No Drawing. Application June 15, 1940, Serial No. 340,783

'4 Claims. (01. 75-168) The invention relates to magnesium base alloys and more particularly concerns an alloy of this nature having a high degree of formability associated with other desirable physical properties, such as good tensile and yield strengths.

Magnesium alloys are being widely used in the structural arts where a-light weight. metal is highly desirable, such for use in making castings, forgings, and the like. However, the use of these alloys in the rolled form to make sheet metal articles requiring forming operations, such as bending, drawing, and the like, has not progressed as rapidly due t the fact that, in general, alloys of good formability or ductility permitting relatively sharp bends to be made without the article developingexternal cranks, usual- 1y have inferior characteristics as regards their tensile and yield strengths.

It is, accordingly, the principal object of the invention to provide a magnesium base alloy which can be made into rolled sheet and the like possessing a sumcient degree of ductility or formability at ordinary temperatures to be sharpcially available, was found to have a yield strength of only 14,000 pounds per square inch in the annealed state, while in the cold rolled state it exhibited a yield strength of 20,000 pounds per square inch. Similarly the tensile strength of my new binary alloy shows improvement over that of commercially pure magnesium treated in a like manner. For example, a specimen of sheet of the 1 per cent lanthanum allay in the annealed state had a tensile strength of 34,000 pounds per square inch, while in the cold rolled state, the alloy had a tensile strength of 33,000 pounds per square inch. Magnesium itself, as commercially available, had a tensile strength of only 28,000 pounds per square inch in the annealed state and 27,000 pounds per square inch in the cold rolled state. The elongation, which serves as a measure of ductility or adaptability for forming operations, of the preferred composition was in the order of 16 per cent in the annealed state, while commercially pure magnesium exhibited an elongation of only ly bent, drawn or otherwise shaped, while having good tensile and yield strengths. I

Other objects and advantages will be apparent as the description of the invention proceeds.

My invention resides in the discovery that a magnesium base alloy composed of from about 0.01 to 6 per cent of lanthanum, the balance being magnesium, possesses the aforementioned properties. The term magnesium," used herein and in the appended claims, is intended to include magnesium containing the ordinary impurities that are found in the commercially pure metal, such as traces of iron, copper, nickel, and silicon. While the property of high strength is manifest over the entire range of composition indicated, I have found that in general an alloy containing from about 1 to 6 per cent of lanthanum possesses the most satisfactory strength and formability characteristics.

A preferred composition having highly desirable ductility for forming operations, as well as exceptionally high yield and tensile strengths is one containing about 1 per cent of lanthanum, the balance being magnesium. As an illustration of the improvement in properties of the new alloy containing 1 per cent lanthanum, annealed specimens of rolled sheet made from this alloy were tested and found to have an average yield strength of 19,000 pounds per square inch, while a specimen of sheet in the cold rolled state was found to have a yield strength of 22,000 pounds per square inch. Magnesium itself, as commer- 7 per cent. Alloys containing higher percentages of the alloying element, suchas from between about 2 to 6 per cent of lanthanum, have fair ductility and markedly higher yield and tensile strengths.

The properties set forth above under the term in the annealed state were obtained by first rolling the alloys at a temperature of 700 F. and thereafter annealing them at various temperatures through a range of from 400 to 800 F. The properties selected were those of the annealed specimens which exhibited the maximum elongation. The properties set forth under the term cold rolled were obtained by subjecting specimens of the alloys which had first been hot rolled at a temperature of 700 F. to additional rolling in the cold state. The properties selected were those of the cold rolled specimens which showed the greatest tensile and yield strengths, while having at least a 1 per cent elongation in 2 inches.

While the new alloy is most useful in wrought "form, such as sheets, due to its formability characteristics, it may also be used for making castings, extruded forms and the like.

The new alloy may be compounded by any of the methods usually employed for melting and alloying metals with magnesium, such as by adding the lanthanum to a bath of molten magnesium, which is preferably protected from oxidation by a suitable flux.

I claim:

1. A magnesium base alloy containing from 0.01 to 6 per cent of lanthanum, the balance being magnesium.

2. A magnesium base alloy containing from 0.1 to 0.5 per cent of lanthanum, the balance being magnesium.

3. A magnesium base alloy containing from 1 to 2 per cent of lanthanum, the balance being magnesium.

4. A magnesium base alloy containing from 0.01 to 6 per cent of lanthanum and characterized by higher yield strength, tensile strength, and Iormability than magnesium without. the

5 lanthanum.

'JOHN C. McDONALD 

